1. Field of the Invention
The present invention relates to a liquid crystal display device.
2. Description of the Related Art
In recent years, liquid crystal display devices are attracting the attention of those skilled in the art since they are thin and light in weight, and are expected to replace conventional CRT display devices.
As an example of a transmission type liquid crystal display device, an active matrix address type liquid crystal which includes a thin film transistor (TFT) formed of amorphous silicon is known. Generally, this type of liquid crystal display device is made up of a transistor matrix array substrate, a filter substrate, and a liquid crystal layer sealed between the two substrates. The array substrate is obtained by arranging the following elements on a glass substrate: a gate electrode, a gate insulation film, an amorphous silicon layer serving as a thin film transistor, a source electrode, a drain electrode, a transparent display electrode plate, a protecting insulation film, etc. Likewise, the filter substrate is obtained by arranging the following elements on a glass substrate: a light-shielding layer, a color filter layer, and a transparent conductive film An orientation layer for orientating liquid crystal molecules in a predetermined direction is provided between the array substrate and the liquid crystal layer. It is also provided between filter substrate and the liquid crystal layer.
In the liquid crystal display device of the above structure, light is emitted toward the liquid crystal layer from a light source located behind the array substrate, and the light which has passed through the liquid crystal layer is directed from the surface of the filter substrate to external regions, so as to display information on the liquid crystal display device.
The amount of light passing through the liquid crystal layer varies in accordance with the condition in which the liquid crystal molecules of the liquid crystal layer facing the transparent display electrode plate are arranged. The condition in which the liquid crystal molecules are arranged is controlled by a voltage or a display potential applied between the electrode plate and the transparent conductive film. To show desirable information or an image on the liquid crystal display device, each picture element of the liquid crystal display device is applied with a predetermined display potential by the TFT.
In the liquid crystal layer, the regions whose liquid crystal transmission factor are controllable are limited to those regions which face the transparent display electrode plate. In other words, the regions which do not face the transparent display electrode plate cannot be controlled or modified with respect to the liquid crystal transmission factor (such regions will hereinafter be referred to as unmodulated regions). To improve the contrast exhibited by the liquid crystal display device, a light-shielding layer is normally formed on those portions of the filter substrate which face the unmodulated regions of the liquid crystal layer, thereby shielding light which may leak from the unmodulated regions. Therefore, the ratio of the area, which can be actually used for showing information, to the entire display area of the display device (in short, the aperture ratio of the display device) is determined by the area on which the light-shielding layer is not formed. Generally, for considering misregistration between the array and filter substrates when they are jointed to each other, this type of display device employs a light-shielding layer wider than the area of the unmodulated regions, and part of the light-shielding layer overlaps the peripheral portions of the display electrode plate.
The performance of the display device may be improved if a large aperture ratio is provided. For this purpose, it is necessary to increase the area of the transparent display electrode plate. However, if the electrode plate is large in area, the space between the electrode plate and the signal lines of the array substrate is inevitably narrow. It is therefore likely that the electrode plate and the signal lines will be short-circuited to each other, either directly or through dust which may enter the space. Accordingly, the display device may have a number of point defects, resulting in the degradation of the manufacturing yield of the display device.
As may be understood from the above, the satisfactory display performance of the display device and the manufacturing yield thereof are incompatible with each other. It is for this reason that a conventional display device cannot employ a display electrode plate having a large area.